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Robert Matthews asks is the Sun just a white-hot ball bearing?

Robert Matthews

12:01AM GMT 12 Nov 2003

Our supposedly middle-aged Sun has been behaving like an adolescent of late, hurling huge clouds of particles at us after its face broke out in spots. Its celestial hissy fit has damaged satellites, sent the occupants of the International Space Station scurrying for cover, and forced aircraft to change routes to avoid excessive cosmic radiation.

The Sun's outburst has also produced some spectacular displays of the Northern Lights in places as far south as Kent and Jersey. Yet the weirdest Earth-bound manifestation to date takes the form of a scientific paper, written by an American physicist. According to Oliver Manuel, a professor of nuclear chemistry at the University of Missouri-Rolla, the recent solar storms are symptomatic of the Sun being made chiefly out of iron.

At first glance, this seems about as plausible as arguing that the Moon is made from cheese. Yet Prof Manuel has published several papers that, he claims, raise serious doubts over the textbook view of the Sun as being a giant ball of hydrogen and helium.

Prof Manuel is happy to go along with the standard idea of the Sun producing heat by fusing together hydrogen nuclei. He claims, however, that this is not the prime source of the Sun's energy. Instead, he says that lurking at the centre of the Sun is an extremely hot remnant of a supernova - the explosion of a giant star that detonated before the solar system was born. Measuring just five to 10 miles across, this remnant makes up most of the mass of the Sun, according to Prof Manuel, and its chief constituent is iron.

In a paper to appear soon in the Journal of Fusion Energy, Prof Manuel argues that his bizarre proposal does a better job than the standard theory of explaining many aspects of the Sun's behaviour, and much else besides. It does seem to provide a neat explanation of why the inner planets, including the Earth, are rocky, while those further away are gas-balls (a mystery whose recalcitrance was noted in this column last month).

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According to Prof Manuel's theory, the inner planets formed closer to the centre of the supernova explosion, where conditions were hotter and thus better-suited to the formation of rocky material.

All very intriguing, and one might expect the scientific community would be keen to know more. Not a bit of it; Prof Manuel has been trying to get others to take his "Iron Sun" theory seriously for decades, without notable success. It is not that the idea is patently barmy. Supernovas are known to produce remnants of the kind he postulates, and the textbooks cheerfully describe them as having a "crust" of pure iron, forged in the nuclear furnace of the huge star that produces the supernova.

The real problem is the huge intellectual investment astronomers have made in the hydrogen-based model of the Sun. After all these years, they are going to need a lot of persuading to give that up and turn to the Iron Sun theory. Or rather, to return to it. For the truth is that astronomers have been here before. Astonishingly enough, the idea that the Sun is chiefly made of iron was the prevailing theory until after the Second World War.

For years the evidence seemed compelling. Sunlight viewed through a spectroscope reveals the presence of a myriad of chemical elements in its atmosphere, especially hydrogen and iron. During the 1920s, astrophysicists trying to explain the Sun's brightness found that the sums worked out if the Sun was around 65 per cent iron and 35 per cent hydrogen.

Annoyingly, however, there was another possibility, with just one per cent iron and 99 per cent hydrogen and helium. This awkward second solution was dealt with in the time-honoured fashion, and swept under the carpet. Then in the mid-1920s, a young English-born astronomer working at Harvard University claimed that the spectrum of sunlight was in fact consistent with this second, hydrogen-rich solution.

In making this outrageous claim, Cecilia Payne had forgotten something: she was a woman. This ensured that she had enormous difficulty persuading her superiors to take her work seriously (at one stage she was funded on the basis of being "equipment"). In her final report she was forced to add the statement that the abundance of hydrogen she had observed was "almost certainly not real". It took another 20 years before Payne's original claim was confirmed, following detailed calculations by the Cambridge astrophysicist Fred Hoyle.

It is doubtless significant that Hoyle's brilliance was matched only by his combativeness. Prof Manuel will surely need that characteristic in abundance if he hopes to persuade the scientific community to do another volte face, and revive the theory of the Iron Sun.